The present invention relates to a novel class of non-oxide, transition metal based ceramics which are capable of intercalating group IA elements therein. These materials have utility as electrodes for batteries, fuel cells, capacitors, electrochromic displays and the like. They may also be used as elements in semiconductor devices, as catalysts, and as structural elements in a variety of specialized devices.
The materials of the present invention are described as being non-oxide ceramics, and within the context of this disclosure the term is meant to refer to compounds of transition metals having one or more of boron, carbon, nitrogen and silicon occupying a number of interstitial sites in their crystalline lattice. As such, they are distinguished from prior art oxide based ceramics. It is to be understood that in some instances, the materials of the present invention may include some minor proportions of oxygen therein, either as a native oxide formed on the surface thereof, or as a minor proportion of oxygen occupying internal sites of the bulk material. Nonetheless, the properties of the materials of the present invention are attributable to the non-oxygen components thereof, and as such, it will be understood that non-oxide ceramics, as defmed herein, may include some small portions of oxygen therein.
It is notable that the materials of the present invention can incorporate group IA elements therein. The group IA elements occupy interstitial sites in the lattice, and may be readily inserted and removed therefrom and such insertion and removal is referred to herein as intercalation. It is further to be noted that as used herein, the term group IA elements is meant to refer to hydrogen group elements of the periodic table.
The materials of the present invention are capable of intercalating large amounts of hydrogen or lithium in relatively small volumes, therefore, they have significant utility as electrodes for batteries, sensors and the like, and as catalysts. The materials of the present invention are low in cost and environmentally benign. Furthermore, they have high electrical conductivities, compared to other ceramics, and manifest good thermal stability. It has been found that the electrochemical potential of these materials can be controlled by varying their stoichiometry, and this feature is significant, insofar as it permits manufacture of electrochemical cells having a controlled discharge profile.
Previously, oxide based ceramic materials have been employed as battery electrodes, and one particular lithium ion battery electrode utilizing oxide based ceramics is disclosed in U.S. Pat. No. 5,110,696. Another such oxide based battery electrode is disclosed in U.S. Pat. No. 5,358,801.
As will be explained hereinbelow, the mechanical, chemical and electrical properties of the materials of the present invention distinguish them from prior art ceramics, and greatly enhance their utility as catalysts, electrodes, and the like.
Also disclosed herein are some novel methods for the fabrication of the materials of the present invention. These and other advantages of the present invention will be readily apparent from the drawings, discussion and description which follow.